The present invention relates to powertrain mounts for motor vehicles, and more particularly to a powertrain mount having a high frequency plunger.
It is desirable to provide motor vehicles with improved operating smoothness by damping and/or isolating powertrain vibrations of the vehicle. A variety of mount assemblies are presently available to inhibit such engine and transmission vibrations. Many of these mount assemblies combine the advantageous properties of elastomeric materials with hydraulic fluids. A hydraulic mount assembly of this type typically includes a reinforced, hollow rubber body that is closed by a resilient diaphragm so as to form a cavity. This cavity is separated into two chambers by a plate. The chambers are in fluid communication through a relatively large central orifice in the plate. The first or primary chamber is formed between the partition plate and the body. The secondary chamber is formed between the plate and the diaphragm.
A decoupler may be positioned in the central passage of the plate to reciprocate in response to the vibrations. The decoupler movement alone accommodates small volume changes in the two chambers. When, for example, the decoupler moves in a direction toward the diaphragm, the volume of the portion of the decoupler cavity in the primary chamber increases and the volume of the portion in the secondary chamber correspondingly decreases, and vice-versa. In this way, for certain small vibratory amplitudes and generally higher frequencies, fluid flow between the chambers is substantially avoided and undesirable hydraulic damping is eliminated. In effect, this decoupler is a passive tuning device.
In addition to the relatively large central passage, an orifice track with a smaller, restricted flow passage is provided extending around the perimeter of the orifice plate. Each end of the track has an opening; one opening communicating with the primary chamber and the other with the secondary chamber. The orifice track provides the hydraulic mount assembly with another passive tuning component, and when combined with the decoupler, provides at least three distinct dynamic operating modes. The particular operating mode is primarily determined by the flow of fluid between the two chambers.
More specifically, small amplitude vibrating input, such as from relatively smooth engine idling or the like, produces no damping due to the action of the decoupler, as explained above. In contrast, large amplitude vibrating inputs, such as large suspension inputs, produce high velocity fluid flow through the orifice track, and an accordingly high level of damping force and desirable control and smoothing action. A third or intermediate operational mode of the mount occurs during medium amplitude inputs experienced in normal driving and resulting in lower velocity fluid flow through the orifice track. In response to the decoupler switching from movement in one direction to another in each of the modes, a limited amount of fluid can bypass the orifice track by moving around the edges of the decoupler, smoothing the transition.
Powertrain mounts are also known which include a plunger. This plunger, also known as an interlock, creates a desirable dip in the dynamic rate of the mount above about 100 Hz. However, mounts with plungers also exhibit an undesirably steep rate increase after the dip.
The present invention is a mount for a powertrain component of a motor vehicle. The mount comprises first and second mounting members, an elastomeric body connected to the first mounting member and connected to the second mounting member, and a plate. The plate defines first and second chambers, and has an orifice for the passage of fluid therethrough. A plunger having at least one hole is connected to the first mounting member, and a compliance member is disposed proximate the at least one hole.
Accordingly, it is an object of the present invention to provide an improved hydraulic-elastomeric mount assembly overcoming the limitations and disadvantages of the prior art.
Another object of the present invention is to provide a fully passively tuned hydraulic mount assembly exhibiting significantly improved high frequency tuning characteristics while maintaining the desired damping for control of high amplitude, low frequency vibrational inputs.
Still another object of the present invention is to provide an improved hydraulic mount assembly including a plunger having a compliance member disposed proximate holes in the plunger.
The foregoing and other features and advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention rather than limiting, the scope of the invention being defined by the appended claims and equivalents thereof.